Compounds known to have antifolate activity are well recognized as chemotherapeutic agents for the treatment of cancer. In particular, compounds in the folic acid family have various activities at the enzymatic level as they inhibit such enzymes as dehydrofolate reductase, folate polyglutamate synthetase, glycinamide ribonucleotide formyltransferase and thymidylate synthetase.
A series of 4-hydroxypyrrolo[2,3-d]pyrimidine-L-glutamic acid derivatives have been disclosed, for example in EP 0434426, and shown to be particularly useful antifolate drugs, among them, pemetrexed disodium heptahydrate of formula I.

Pemetrexed disodium salt heptahydrate is marketed by Eli Lilly and Company under the trade name ALIMTA® as a sterile lyophilized powder for intravenous administration. This member of the folic acid family has been approved for treatment of malignant pleural mesothelioma and for second-line treatment of non small cell lung cancer. See Physicians' Desk Reference, 60th ed., pp. 1722-1728 (2006). The commercial product is reported to be a lyophilized powder of heptahydrate pemetrexed disodium and mannitol.
U.S. Pat. No. 7,138,521 discloses crystalline pemetrexed disodium heptahydrate. This heptahydrate form is prepared from N-[4-[2-(2-Amino-4,7-dihydro-4-oxo-3H-pyrrolo[2,3-d]pyrimidin-5-yl)ethyl]benzoyl]L-glutamic acid diethylester p-toluenesulfonic acid salt, which is saponified at a pH of between 2.5 to 3.5 to give N-[4-[2(2-amino-4,7-dihydro-4-oxo-1H-pyrrolo[2,3-d]pyrimidin-5-yl)ethyl]benzoyl]-L-glutamic acid (“pemetrexed diacid”), of the following Formula II:
The pemetrexed diacid is isolated as a wet cake and then combined with 2 to 3 equivalents of sodium hydroxide at a pH of between 7 and 9. The resulting pemetrexed disodium heptahydrate is then isolated from the reaction mixture by precipitation using acetone. The isolated pemetrexed disodium heptahydrate is then used to prepare the pharmaceutical composition.
International PCT publication WO 01/14379 discloses crystalline hydrated pemetrexed disodium and methods for preparing it from a carboxy-protected N-[4-[2-(2-amino-4,7-dihydro-4-oxo-3H-pyrrolo[2,3-d]pyrimidin-5-yl)ethyl]benzoyl]L-glutamic acid. The method includes reacting the carboxy-protected pemetrexed diacid with sodium hydroxide to obtain the pemetrexed disodium, without the need to pass through and to isolate pemetrexed diacid, which is stated to be “highly toxic” and to “requir[e] special handling measures and equipment.” The obtained pemetrexed disodium is then used to prepare the pharmaceutical composition.
There is a need in the art for a method to produce the lyophilized disodium salt of pemetrexed diacid directly from pemetrexed diacid, i.e., without isolating the disodium salt of pemetrexed diacid.